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Research Papers

Computational Fluid Dynamics Evaluation of Equivalency in Hemodynamic Alterations Between Driver, Integrity, and Similar Stents Implanted Into an Idealized Coronary Artery

[+] Author and Article Information
Timothy J. Gundert

Department of Biomedical Engineering,
Marquette University,
1515 West Wisconsin Avenue,
Milwaukee, WI 53233

Ronak J. Dholakia

Department of Neurological Surgery,
Stony Brook University Medical Center,
Stony Brook, NY 11794

Dennis McMahon

Medtronic CardioVascular,
3576 Unocal Place,
Santa Rosa, CA 95403

John F. LaDisa

Department of Biomedical Engineering,
Marquette University,
1515 West Wisconsin Avenue,
Milwaukee, WI 53233;
Department of Medicine,
Division of Cardiovascular Medicine,
Medical College of Wisconsin,
8701 Watertown Plank Road,
Milwaukee, WI 53226
e-mail: john.ladisa@marquette.edu

1Corresponding author.

Manuscript received July 24, 2012; final manuscript received January 2, 2013; published online February 4, 2013. Assoc. Editor: Keefe B. Manning.

J. Med. Devices 7(1), 011004 (Feb 04, 2013) (10 pages) Paper No: MED-12-1093; doi: 10.1115/1.4023413 History: Received July 24, 2012; Revised January 02, 2013

We tested the hypothesis that a slight modification in fabrication from the Driver to the Integrity stent (Medtronic) results in nearly equivalent distributions of wall shear stress (WSS) and mean exposure time (MET), reflective of flow stagnation, and that these differences are considerably less than the Multi-Link Vision (Abbott Vascular) or BX Velocity (Cordis) bare metal stents when evaluated by computational fluid dynamics (CFD). Arteries were modeled as idealized straight rigid vessels without lesions. Two vessel diameters (2.25 and 3.0 mm) were studied for each stent and 2.75 mm diameter Integrity stents were also modeled to quantify the impact from best- and worst-case orientations of the stent struts relative to the primary blood flow direction. All stents were 18 mm in length and over-deployed by 10%. The results indicated that, regardless of diameter, the BX Velocity stents had the greatest percentage of the vessel exposed to adverse WSS followed by the Vision, Integrity, and Driver stents. In general, when strut thickness and stent:lumen ratio are similar, the orientation of struts is a determining factor for deleterious flow patterns. For a given stent, the number of struts was a larger determinant of adverse WSS and MET than strut orientation, suggesting that favorable blood flow patterns can be achieved by limiting struts to those providing adequate scaffolding. In conclusion, the Driver and Integrity stents both limit their number of linkages to those which provide adequate scaffolding while also maintaining similar strut thickness and stent:lumen ratios. The Integrity stent also imparts a slight helical velocity component. The modest difference in the fabrication approach between the Driver and Integrity stents is, therefore, not hemodynamically substantial in this idealized analysis, particularly relative to potentially adverse flow conditions introduced by the other stents modeled. This data was used in conjunction with associated regulatory filings and submitted to the FDA as part of the documents facilitating the recent approval for sale of the Resolute Integrity stent in the United States.

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Figures

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Fig. 1

Computer-aided design representations of the Integrity (Medtronic), Driver (Medtronic), Multi-Link Vision (Abbott Vascular), and BX Velocity (Cordis) stents before ((left) with stents longitudinally sectioned for clarity), and after virtual implantation into an idealized artery using 10% over-deployment (right)

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Fig. 2

Final computational meshes used for each stent and a wide angle view showing increased mesh density within the stented region, as compared to the proximal and distal unstented regions

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Fig. 3

Blood flow at the outlet of the 3 mm diameter BX Velocity stent (top) and corresponding blood pressure (middle). Gridlines have been added to delineate each cardiac cycle and evolution of blood flow and pressure values between successive cardiac cycles. (inset) The residual error for the entire simulation is also shown along with that after the first four time steps (bottom). These tracings are similar for all of the stents modeled.

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Fig. 4

Magnitude-weighted near-wall velocity vectors (range: 0 to 4 cm/s) from the middle portions of each 2.25 mm diameter vessel. Vectors have been superimposed on the model surface and stent struts have been removed for clarity.

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Fig. 5

Mean exposure time (MET: range 0 to 0.45 s/cm) providing an indication of the average duration particles reside within various regions of each 2.25 mm diameter vessel. The portion of vessels shown (top) are from the middle of the stented region. (A) Longitudinal, and (B) generally circumferential slices are provided to qualitatively analyze the impact of strut thickness, proximity, and profile on the MET.

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Fig. 6

Time-averaged wall shear stress (TAWSS) normalized by the average wall shear stress in the proximal portion of each 3.0 mm diameter vessel

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Fig. 7

Time-averaged wall shear stress (TAWSS) normalized by the average wall shear stress in the proximal portion of each 2.25 mm diameter vessel

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Fig. 8

Histograms of the TAWSS within proximal (top), center (middle), and distal (bottom) intrastrut areas of each stent. It is desirable for histogram curves to have a large amount of their intrastrut area exposed to greater normalized time-averaged wall shear stress.

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Fig. 9

Instantaneous distributions of wall shear stress at three locations within intrastrut regions of Driver and Integrity stents. Tracings between the stents are indistinguishable at locations ‘A’ and ‘B,’ but slight differences in the relative proximity of struts at location ‘C’ causes modest differences in instantaneous values.

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Fig. 10

Time-averaged wall shear stress (TAWSS) normalized by the average wall shear stress in the proximal portion of the 2.25, 2.75, and 3.00 mm vessels containing Integrity stents with 7.5 crowns (2.2.5 and 2.75 mm) or 9.5 crowns (2.75 undersized vessel and 3.00 mm)

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